Self-Heating Effect Investigation On 14nm FinFET And Its Thermal Modeling

With the dramatic development of the integrated circuit industry,the feature size of semiconductor devices has been reduced to sub-20 nm nodes,and the increase in chip integration has brought greater power density.Meanwhile,in order to suppress the short channel effects caused by device dimension shrinking,new device structures(e.g.,FinFETs,silicon-on-insulator(SOI)and gate-all-around(GAA)structure)and new materials(e.g.,SiGe with low thermal conductivity and high-k gate dielectric layers)are introduced into traditional silicon-based MOS devices.Although these advanced technologies have made it possible to continue the development of Moore's Law,their inefficient heat dissipation ability would make the heat difficult to dissipate,resulting in serious self-heating effect(SHE).The effect of large power density makes the device temperature rise rapidly,and the electrical characteristics and reliability of the device deteriorate,which affects the circuit performance and reduces the lifetime of the chip.Nanoscale FinFET has become the core device in sub-20 nm process and has been applied to sub-10 nm technology nodes due to its excellent electrostatic control and good CMOS process compatibility.However,its narrow 3D fin structure results in the heat accumulation in the channel.In SOI FinFETs,the buried oxide layer with low thermal conductivity becomes a barrier of the heat flow path.The self-heating effect becomes a key difficulty under the advanced technology node,thus it is important to analyze SHE accurately in FinFETs for better electrical characteristics and device reliability.In this dissertation,focusing on the problems and challenges brought by SHE in nanoscale FinFETs,the bulk FinFETs and SOI FinFETs are adopted to investigate thermal characteristics by means of simulation,thermal analysis,modeling and device optimization.The main contents and achievements are summarized as follows:1)Based on the Sentaurus TCAD simulation of SHE in 14 nm FinFETs,the position of the peak temperature and main heat dissipation paths are clarified.The structural parameters,thermal conductivity,ambient temperature and concentration in source/drain extension region dependence of SHE and the on-state current are investigated systematically.The results show that: the smaller channel length and width would cause more severe phonon-boundary scattering,which results in more serious SHE and the degradation of on-state current;the thicker oxide layer and the longer source/drain extension region would result in greater thermal resistance;the higher thermal conductivity of the sidewall can reduce the device peak temperature and this is a more pronounced effect on the SOI FinFET,while the thermal conductivity of the oxide layer has little effect on SHE;the increase in the ambient temperature exacerbates the SHE and degradation of device electrical characteristics.2)2D thermal diffusion quations of source/drain,source/drain extension and gate region are established including corresponding boundary conditions to obtain the temperature distribution and peak temperature of the active region in the single-fin bulk FinFETs with the good understanding of the physical mechanism of heat transfer(Max error is 4.35 K and RMS error is 3.05K).Furthermore,considering the thermal coupling between the fins and the influence of metal contacts,the compact model of SHE dependent on device dimensions and thermal conductivities is established.The validated thermal resistance model can predict the variations of SHE with different fin height,fin number and fin spacing,which can also optimize the SHE of the 14 nm technology node(Max error is 4.62% and prediction results errors are all within 5%).3)It is proposed that device's SHE can be effectively alleviated by increasing the source/drain contact areas.For the multi-fin structure devices,it is also proposed that the use of gate dielectric materials with smaller boundary thermal resistance is beneficial to heat dissipation to the gate,which alleviates the device self-heating effect.In summary,the numerical analysis of the SHE in FinFETs,the establishment of the device structure dependent thermal model,and the proposed optimization for the SHE can provide an important reference for the design of the FinFET circuit.